A polarizing sheet or polarizing film functions in general to convert natural light into polarized light. Such polarizing function may be embodied using a material with which a polarizing sheet is dyed. A liquid crystal display generally has an iodine type polarizing film dyed with iodine, as a polarizing material.
Such an iodine type polarizing film is dyed using dichroic iodine or dichroic dyes, oriented in a predetermined direction through, for example, uniaxial drawing (or orientation) and widely used to manufacture LCDs. For instance, a process of uniaxially orienting an un-oriented PVA film in an aqueous solution and then dipping the oriented PVA film in a solution containing iodine and/or potassium iodide, a process of dipping an un-oriented PVA film in a solution containing iodine and/or potassium iodide then uniaxially orienting the treated PVA film, a process of uniaxially orienting an un-oriented PVA film in a solution containing iodine and/or potassium iodide, a process of uniaxially orienting an un-oriented PVA film in a dried state and then dipping the oriented PVA film in a solution containing iodine and/or potassium iodide, and the like, may be used to prepare a polarizing film.
The PVA film having iodine adsorbed and oriented therein may be subjected to post-treatment through water washing or drying to thereby obtain a polarizing film and, by laminating a protective film to at least one side of the formed polarizing film, a polarizing sheet may be fabricated as a final product. Meanwhile, in the case where the PVA film is changed (replaced) during manufacture of the polarizing sheet, a sample is taken by preparing a polarizing film through trial operation and then cutting the polarizing film, followed by measuring a transmittance of the sample. Thereafter, in order to comply with standard specifications, the sample is generally treated by applying process factors, adding subsidiary materials thereto, and/or diluting the sample.
However, the method of measuring transmittance of a polarizing film after preparing the same through trial operation as described above entails problems of increasing PVA film loss and production cost due to shut-down of a production line in order to measure the transmittance. Furthermore, considering that the polarizing film is commonly prepared through a continuous process, consumption of a large amount of PVA film cannot be avoided during measurement of transmittance.
Accordingly, there is a strong demand for a novel apparatus capable of preparing a polarizing film so as to solve problems of the conventional art described above and minimize loss of materials when a PVA film is replaced.